1. Field of the Invention
The present invention relates to a light emitting and receiving circuit using a light emitting diode, and a camera and an optical device using the light emitting and receiving circuit.
2. Description of the Related Art
For example, in various optical devices such as a camera, there have been used photometer elements (lightxe2x80x94receiving elements) that detect light to detect its intensity or the like. Up to now, as the photometer elements, there have been employed CdS (cadmium sulfide), a photo-diode or the like. All of them are so designed as to detect an incident light as a photoelectric current.
Out of them, CdS is poor in linearity with respect to the luminance of detected light but can detect the light with a simple circuit. For that reason, CdS has been widely used from the viewpoint of the simple structure. On the contrary, the photo-diode has such a characteristic that it is excellent in the linearity with respect to the luminance of received light. Also, because the dynamic arrange is wide, it is possible to detect the light with high accuracy by using an operational amplifier. However, in the case of using the photo-diode, its circuit structure becomes expensive as compared with CdS. Both of those CdS and photo-diode are devices adapted to measure the luminance or illuminance of an object to be photographed, and cannot display the luminance or illuminance.
On the contrary, there is an LED (light emitting diode) which has been widely used as a welfare display element. The LED is used as a pilot lamp or a display device. In the case where the LED is used as the display device such as a numeric display device, the elements of 7 segments are combined in a state where two #-shapes are arranged (8-shaped). As a result, a desired numeral is displayed by allowing a current to flow in given segments.
As described above, the photo-diode is used only as the light receiving element whereas the LED is used only as the light emitting element (display element). Under those circumstances, in the case where the optical device is provided with both of the photometry function and the display function, the structure in which the photo-diode and the LED are separately provided must be applied. For that reason, the space efficiency is lowered, and the costs are increased because both of those elements are employed.
However, both of the photo-diode and the LED are basically semiconductors having a p-n junction. Consequently, the structure in which the LED which functions as the light emitting element, can also serve as the light receiving element, is desirable from the viewpoints of the above-described space efficiency and cost.
The present invention has been made in view of the above circumstances, and therefore an object of the present invention is to provide a light emitting and receiving circuit, and a camera and an optical device which can have high space efficiency and the low cost.
Another object of the present invention is to provide a light emitting and receiving circuit, and a camera and an optical device which are capable of using an LED as the light receiving element.
Still another object of the present invention is to provide a light emitting and receiving circuit, and a camera and an optical device that is capable of adjusting the light emitting luminance of the LED so as to be fitted to the brightness of environments where the LED is used.
In order to achieve the above objects, according to one preferred example of the present invention, there is provided a light emitting and receiving circuit which has a light emitting function as well as a light receiving function, comprising:
a light emitting diode with a p-n junction;
a circuit using said light emitting diode as a light emitting element; and
a circuit using said light emitting diode as a light receiving element that measures the intensity of a light.
Also, according to another aspect of the present invention, there is provided a light emitting and receiving circuit which has a light emitting function and a light receiving function, comprising:
a light emitting diode with a p-n junction; and
switching means connected to said light emitting diode for switching an operating state between a light receiving state where a photoelectromotive force is generated in a direction of biasing the p-n junction when receiving a light, and a light emitting state where a forward voltage is applied to said light emitting diode to emit a light, according to at least one control signal.
Further, according to still another aspect of the present invention, there is provided a light emitting and receiving circuit which has a light emitting function and a light receiving function, comprising:
a light emitting diode with a p-n junction;
switching means for switching an operating state between a light receiving state where a photoelectromotive force is generated in a direction of biasing the p-n junction of said light emitting diode when receiving a light, and a light emitting state where a forward voltage is applied to said light emitting diode to emit a light, according to at least one control signal; and
light emitting luminance control means for controlling the forward voltage which is applied to said light emitting diode on the basis of the light detection result from said light emitting diode, when said light emitting diode is used to emit a light.
Still further, according to yet still another aspect of the present invention, there is provided a camera comprising:
a light emitting diode used as a display element with a p-n junction; and
switching means connected to said light emitting diode for switching an operating state between a light receiving state where a photoelectromotive force is generated in a direction of biasing the p-n junction when receiving a light, and a light emitting state where a forward voltage is applied to said light emitting diode to emit a light according to at least one control signal;
wherein said switching means is so controlled as to be set first in the light emitting state at the time of photographing, and then in the light receiving state to conduct photometry.
Still further, according to yet still another aspect of the present invention, there is provided an optical device comprising:
a light emitting diode used as a display element with a p-n junction; and
switching means connected to said light emitting diode for switching an operating state between a light receiving state where a photoelectromotive force is generated in a direction of biasing the p-n junction when receiving a light, and a light emitting state where a forward voltage is applied to said light emitting diode to emit a light according to at least one control signal;
wherein said switching means is so controlled as to be set first in the light emitting state at the time of photographing and then in the light receiving state to conduct photometry.